The present invention relates to magnetic bearings and, more particularly, to an active magnetic bearing for use in various applications, including satellites and other space applications, that uses a reluctance centering effect to provide axial control of a rotating shaft.
Magnetic bearings suspend a rotational body, such as a rotor, with magnetic force in a non-contact fashion. That is, instead of the physically supporting the rotor using lubricated bearings that are in physical contact with the rotor, various magnets are spaced radially around the rotor and the magnetic forces supplied by the magnets suspend the rotor without any physical contact. In order to provide stable support for the rotor, the magnetic bearing suspends the rotor within five degrees-of-freedom.
Generally, there are two categories of magnetic bearings, passive magnetic bearings and active magnetic bearings. Passive magnetic bearings are the simplest type, and use permanent magnets or fixed strength electromagnets to support the rotor. Thus, the properties of the bearing, such as the magnetic field strength, may not be controlled during operation. Conversely, active magnetic bearings are configured such that the magnetic field strength of the bearing is controllable during operation. To accomplish this, at least one active magnetic bearing channel is provided for each degree-of-freedom of the shaft. An active magnetic bearing channel includes a position sensor, a controller operating according to a predetermined control law, and an electromagnetic actuator. In general, the position sensor senses the position of the shaft and supplies a signal representative of its position to the controller. The controller, in accordance with the predetermined control law, then supplies the appropriate current magnitude to the electromagnetic actuator, which in turn generates an attractive magnetic force to correct the position of the shaft.
Various active magnetic bearing assembly configurations are presently known for controlling a shaft within five degrees-of-freedom. The active magnetic bearing assembly configurations used most prominently are: (1) independent radial and axial bearings; (2) conical bearings; and (3) combination bearings. Each of these different configurations may have certain drawbacks. For example, if independent radial axial bearings are used, then the overall size, or physical package, of the system is relatively large. Conical bearings may use eight drive channels to provide control within five degrees-of-freedom, and provide space savings relative to the use of independent radial and axial bearings. However, conical bearings may suffer from temperature sensitivity, and cross-coupling of radial and axial channels. Finally, while combination bearings may also provide space savings relative to the use of independent radial and axial bearings, the assembly of this bearing configuration may be relatively complex.
Thus, there is a need for an active magnetic bearing assembly that provides the space savings and relatively simple assembly that a conical bearing provides, while simultaneously exhibiting minimal temperature sensitivity. The present invention addresses these needs.
The present invention provides an active magnetic bearing assembly that does not require the use of either separate axial bearing or a combination bearing and thus provides significant space savings and bearing commonality. The bearing also has minimal temperature sensitivity.
In one embodiment of the present invention, and by way of example only, an active magnetic bearing assembly for rotationally mounting a shaft in a non-contact manner includes a first bearing rotor, a first stator assembly, a second bearing rotor, and a second stator assembly. The first bearing rotor has at least a first pole face and a second pole face. The first stator assembly is spaced radially outwardly of the first bearing rotor and has at least a first pole face and a second pole face that are axially offset from the first bearing rotor first pole face and second pole face, respectively, by a first predetermined distance in a first direction. The second bearing rotor has at least a first pole face and a second pole face. The second stator assembly is spaced radially outwardly of the second bearing rotor and has at least a first pole face and a second pole face that are axially offset from the second bearing rotor first pole face and second pole face, respectively, by a second predetermined distance and in a second predetermined direction that is opposite the first predetermined direction.
In another embodiment of the present invention, an energy storage flywheel assembly includes a shaft, a flywheel, and an active magnetic bearing assembly. The flywheel is coupled to the shaft, and the active magnetic bearing assembly rotationally mounts the shaft in a non-contact manner. The magnetic bearing assembly includes a first bearing rotor, a first stator assembly, a second bearing rotor, and a second stator assembly. The first bearing rotor has at least a first pole face and a second pole face. The first stator assembly is spaced radially outwardly of the first bearing rotor and has at least a first pole face and a second pole face that are axially offset from the first bearing rotor first pole face and second pole face, respectively, by a first predetermined distance in a first direction. The second bearing rotor has at least a first pole face and a second pole face. The second stator assembly is spaced radially outwardly of the second bearing rotor and has at least a first pole face and a second pole face that are axially offset from the second bearing rotor first pole face and second pole face, respectively, by a second predetermined distance and in a second predetermined direction that is opposite the first predetermined direction.
In yet another embodiment of the present invention, an apparatus for imparting rotational motion to a shaft includes a shaft, a rotational motion imparting device, and an active magnetic bearing assembly. The rotational motion imparting device is coupled to the shaft, and the active magnetic bearing assembly rotationally mounts the shaft in a non-contact manner. The magnetic bearing assembly includes a first bearing rotor, a first stator assembly, a second bearing rotor, and a second stator assembly. The first bearing rotor has at least a first pole face and a second pole face. The first stator assembly is spaced radially outwardly of the first bearing rotor and has at least a first pole face and a second pole face that are axially offset from the first bearing rotor first pole face and second pole face, respectively, by a first predetermined distance in a first direction. The second bearing rotor has at least a first pole face and a second pole face. The second stator assembly is spaced radially outwardly of the second bearing rotor and has at least a first pole face and a second pole face that are axially offset from the second bearing rotor first pole face and second pole face, respectively, by a second predetermined distance and in a second predetermined direction that is opposite the first predetermined direction.
In still a further embodiment of the present invention, a satellite includes a housing, a component within the housing having a shaft, and an active magnetic bearing. The active magnetic bearing assembly rotationally mounts the shaft in a non-contact manner and includes a first bearing rotor, a first stator assembly, a second bearing rotor, and a second stator assembly. The first bearing rotor has at least a first pole face and a second pole face. The first stator assembly is spaced radially outwardly of the first bearing rotor and has at least a first pole face and a second pole face that are axially offset from the first bearing rotor first pole face and second pole face, respectively, by a first predetermined distance in a first direction. The second bearing rotor has at least a first pole face and a second pole face. The second stator assembly is spaced radially outwardly of the second bearing rotor and has at least a first pole face and a second pole face that are axially offset from the second bearing rotor first pole face and second pole face, respectively, by a second predetermined distance and in a second predetermined direction that is opposite the first predetermined direction.
Other independent features and advantages of the preferred sensor will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.